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  <title>Document</title>
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<script>
  var arr = function (firstList, secondList) {
    let i = 0, j = 0, ans = [], A = firstList, B = secondList;
    while (i < A.length && j < B.length) {
      //左边取大的一个
      let left = Math.max(A[i][0], B[j][0]),
        //右边取小的一个
        right = Math.min(A[i][1], B[j][1]);
      if (left <= right) ans.push([left, right])
      A[i][1] > B[j][1] ? j++ : i++
    }
    return ans
  };
  console.log(arr(firstList = [[0, 2], [5, 10], [13, 23], [24, 25]], secondList =
    [[1, 5], [8, 12], [15, 24], [25, 26]]));
</script>

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